Controls for centrifugal compressors having spin vanes in their inlets



CONTROLS FOR CENTRIFUGAL COMPRESSORS HAVING Nov. 7, 1967 R. PLASTER 3,350,897

SPIN VANES IN THEIR INLETS Filed Jan. 11, 1966 5 Sheets-Sheet 2 33 4 42 52 RETURN MA ya 34. 33-"- SA B 36 84 89 FIGS.

as a9 |NVENTOR= ROBERT L. PLASTER,

BYW :2 212% ATTORNEY Nov. 7, 1967 Filed Jan. 11, 1966 R. L. PLASTER CONTROLS FOR CENTRIFUGAL COMPRESSORS HAVING SPIN VANES IN THEIR INLETS 3 Sheets-Sheet 5 F I G. 8

lNVENTOR= ROBERT 1.. PLASTER, BY QQM ATTORNEY United States Patent 3,350,897 CONTROLS FOR CENTRIFUGAL COMPRESSORS HAVING SPIN VANES IN THEIR INLETS Robert L. Plaster, Staunton, Va., assignor to Westinghouse- Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 11, 1966, Ser. No. 519,876 Claims. (Cl. 6220 9) ABSTRACT OF THE DISCLOSURE Spin vanes of a centrifugal compressor are adjusted by a piston slidable within a cylinder. A first two-way valve is adjusted by a first solenoid coil, when deenergized, to supply fluid into one end of the cylinder to move the piston in one direction to adjust the vanes towards open positions. A second two-way valve is adjusted :by a second solenoid coil, when deenergized, to supply fluid into the other end of the cylinder to move the piston in the opposite direction to adjust the vanes towards closed positions. Normally both coils are deenergized so that fluid is supplied into both ends of the cylinder to maintain the piston in a hold position. When the first coil is energized, with the second coil deenergized, it adjusts the first valve to exhaust the fluid it supplied into the cylinder, permitting the piston to move the vanes towards closed positions. When the second coil is energized, with the first coil deenergized, it adjusts the second valve to exhaust the fluid it supplied into the cylinder, permitting the piston to move the vanes towards open positions. A thermostat has a low temperature switch for energizing the second coil, and has a high temperature switch for energizing the first coil. An overload control for the compressor motor has a switch for energizing the first coil when the motor is overloaded. A suction pressure control has a switch for energizing the first coil when the suction gas pressure is low.

This invention relates to controls for centrifugal refrigerant compressors having spin vanes in their inlets, and has as objects to simplify and reduce the costs of such controls.

Centrifugal refrigerant compressors such as are disclosed in the copending application of R. W. Wolfe and R. R. Young, Ser. No. 280,606, filed May 15, 1963, now patent No. 3,251,539, have spin inducing vanes in their inlets for capacity control. When the load on such a compressor is relatively small, its spin vanes are adjusted by a thermostat to increase the spin in the gas entering the compressor inlet, and when the load is relatively large, the spin vanes are adjusted to decrease the spin or to positions in which they induce no spin. Hunting of the spin vanes may occur about the set point of the thermostat, and the most common method of preventing such hunting has been to use feeler rods which contact the vane adjusting mechanisms and respond to over-shoot, and to control feedback circuits by using such rods. Such a method requires that feeler rods and wires extend through compressor casings, and does not operate satisfactorily when loads vary over a wide range.

My copending application, Ser. No. 404,338, filed Oct.

16, 1964, now Patent No. 3,248,896, discloses a control This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a diagrammatic view of a refrigeration system embodying this invention;

FIGS. 2a-2c are diagrammatic views of relays used for controlling the system of FIG. 1;

FIG. 3 is a simplified electrical circuit schematic of the electrical controls of the system;

FIG. 4 is a digarammatic view of the mechanism for the adjustment of the spin vanes of the compressor of FIG. 1;

FIG. 5 is an enlarged, sectional view of the two, interconnected, solenoid adjusted valves of FIG. 4, the pistons of the valves being shown in the positions they take when the solenoid coils of the two valves are deenergized;

FIG. 6 is a view similar to FIG. 5 except that one solenoid coil, the left one, is energized;

FIG. 7 is a view similar to FIG. 5 except that the other solenoid coil, the right one, is energized, and

FIG. 8 is a diagrammatic view showing a modification of the mechanism shown by FIG. 4.

Referring first to FIG. 1, a centrifugal refrigerant compressor C, driven by an electric motor CM, has its outlet connected by tube 10 to a condenser 11. The condenser 11 is connected by tube 12 and expansion valve EV to the refrigerant inlet of a shell-and-tube evaporator 14, the refrigerant outlet of which is connected by suction gas tube 15 to the inlet of the compressor C. The tube 15 contains a conventional low pressure control LPC having a normally open switch LPCS.

The evaporator 14 has a water inlet tube 16 and a Water outlet tube 17, water being chilled within the evaporator and supplied to local air coolers which are not shown. A thermostat bulb 18 is in contact with the tube 17, and is connected by a capillary tube 19 to a conventional twostage thermostat T. The thermostat T has a low temperature switch LTS and a high temperature switch HTS with an adjustable dead-band between the operating points of its two switches. Such a thermostat may be a Penn Series 219 thermostat manufactured by Penn Controls, Inc. of Goshen, Ind., and described in its Bulletin 219T2X.

Referring now to FIGS. 2a-2c, a relay R has normally open switches RS1 and RS3 which close when the relay is energized, and has a normally closed switch RS2 which opens when the relay is energized. A control relay CR1 has a normally closed switch LCS which opens when the relay CR1 is energized. Another control relay CR2 has a normally open switch HCS which closes when the relay CR2 is energized.

Referring now to FIG. 4, the compressor C, a fraginto an annular slot 25 in annular piston 26. The piston I 26 has outer surfaces in slidable contact with surfaces of compressor wall 27, and has inner surfaces in slidable contact with surfaces of the wall 23. The right end portion of the piston 26 has an enlargement 29 with a cylinder passage portion 30 formed by portions ofthe walls 23 and 27 to the right of its right end, and with a cylinder passage portion 31 formed within the wall 27 to the left of the left end of the piston. A fluid tube 33 connects With the passage portion 30, and a fluid tube 34 connects with the passage portion 31.

A two-way valve VA, adjustable by a solenoid coil SA is connected to the tube 34, to a fluid return tube 42, and to fluid supply tube 36, the latter being connected to a conventional source of fluid under pressure, and which may be an oil pump driven by the motor CM or by a separate motor, the source of the fluid under pressure not being shown. The fluid return tube 42 would be connected to the input of such a source. Another two-way valve VB, adjustable by a solenoid coil SB, is connected to the tubes 33 and 42 and the tube 36. A conventional one-way valve VC, adjustable by a conventional solenoid SC is connected to the tubes 36 and 33.

Referring now to FIGS. 7, the valves VA and VB are of non-magnetic material except for their piston rods which will be described later, and have chambers 45 and 46 respectively, the tops of which are connected to the tubes 34'and 33 respectively. The bottoms of the chambers 45 and 46 connect through tubes 47 and 48 respectively, 'withf-the tube '36. A valve seat 50 is formed where the tube 47 connects with the chamber 45. A valve seat 51 is formed where the tube 48 connects with the chamber 46. The fluid return tube 42 connects with a tube 52 which extends through the interiors of the chambers 45 and 46. The tube 52 has a downwardly turned portion 54 within the chamber 45, and has a valve seat 55 at its bottom which is aligned with and spaced vertically above the valve seat 50. The tube 52 has a downwardly turned portion 56 within the chamber 46, and has a valve seat 57 at its bottom which is aligned with and spaced vertically above the valve seat 51.

The tube 47 contains a magnetic piston rod 57 slidable vertically in perforated guides 58 attached to the wall of the tube 47. A disc 60 having a smaller diameter than the internal diameter of the tube 47 is attached to the bottom of the rod 57, and a perforated disc 61 is attached to the wall of the tube 47 below the disc 60. A coiled spring 62 extends between the discs 60 and 61, and biases the piston rod 57 upwardly. A valve disc 63 is attached to the top of the rod 57. The solenoid coil SA extends around the tube 47 and the piston rod 57. When the coil SA is deenergized as shown by FIG. 5, the spring 62 causes the disc 63 to be seated on the valve seat 55. When the coil SA is energized as shown by FIG. 6, the piston rod 57 is retracted and moves the disc 63 from the valve seat 55 onto the valve seat 50.

The tube 48 contains a magnetic piston rod 67 slidable vertically in perforated guides 68 attached to the wall of the tube 48. A disc 70 having a smaller diameter than the internal diameter of the tube 48 is attached to the bottom of the rod 67, and a perforated disc 71 is attached to the wall of the tube 48 below the disc 70. A coiled spring 72 extends between the discs 70 and 71, and biases the piston rod 67 upwardly. A valve disc 73 is attached to the top of the rod 67. The solenoid coil SB extends around the tube 48 and the rod 67. When the coil SB is deenergized as shown by FIG. 5, the spring 72 causes the valve disc 73 to be seated on the valve seat 57. When the coil SB is energized as shown by FIG. 7, the piston rod 67 is retracted, and the valve disc 73 is moved from the valve seat 57 onto the valve seat 51. When both coils SA and SB are deenergized as shown by FIG. 5, fluid from the supply tube 36 flows through the tubes 47 and 48, the chambers 45 and 46 respectively, and the tubes 34 and 33 respectively, into the cylinder passages 31 and 30 respectively, against both fluid responsive surfaces of the piston 26, maintaining the latter against movement in either direction in a hold position.

When the coil SA is energized with the coil SB deenergized as shown by FIG. 6, compressed fluid from the tube 36 flows through the tube 48 into the chamber 46 of the valve VB, and through the tube 33 into the cylinder passage 30. Previously compressed fluid from the cylinder passage 31 flows through the tube 34 into the chamber 45 of the valve VA, and from the latter through the valve seat 55, the tube portion 54 and the tube 52 into the return tube 42, permitting the compressed fluid supplied into the cylinder passage 30 to move the piston 26 to the left to adjust the spin vanes 21 towards closed positions.

When the coil SB is energized with the coil SA deenergized as shown by FIG. 7, compressed fluid from the tube 36 flows through the tube 47 into the chamber 45 of the valve VA, and through the tube 34 into the cylinder passage 31. Previously compressed fluid from the cylinder passage 30 flows through the tube 33 into the chamber 46 of the valve VA, and from the latter through the valve seat 57, the tube portion 56 and the tube 52 into the return tube 42, permitting the compressed fluid supplied into the cylinder passage 31 to move the piston 26 to the right to adjust the spin vanes 21 towards open positions.

When the solenoid SC is energized, it opens the valve VC which supplies compressed fluid from the tube 36 directly into the tube 33 and the cylinder passage 30.

Referring now to FIG. 3, the compressor motor CM is connected by a wire 79 to electric supply line L1 and by wire 90 to electric supply line L2, the usual motor starter and its switches not being shown. A current transformer winding 91 extends around the wire 79 and is connected to a conventional motor load control 92, a simplified circuit of which is shown by the drawings of my previously mentioned application. The control relays CR1 and CR2 are conected to the low current and the high current outputs respectively, of the control 92. One end of the relay R is connected to the line L2, and its other end is connected through the switches HCS and LPCS connected in parallel, to the line L1. The other end of the relay R is also connected through the switches RS1, HTS and RS2 in series, to the line L1. The solenoid coil SA is connected to the line L2 and through the switch RS1 to the other end of the relay R. The solenoid coil SB is connected to the line L2 and through the series connected switches LCS, LTS and RS2 to the line L1. The solenoid SC is connected to the line L2 and through the switch RS3 to the line L1.

The tube 47 where it connects with the tube 36 has inwardly converging walls 80 forming a converging passage opposite correspondingly inwardly converging head 81 of screw threaded in wall 83 of the tube 36. The screw 82 has a slotted outer end 84. Likewise, the tube 48 where it connects with the tube 36 has an inwardly converging wall 86 forming a converging passage opposite correspondingly inwardly converging head 87 of screw 88 threaded in the wall 83. The screw 87 has a slotted outer end 89. The screws 82 and 86 can be adjusted by a screwdriver for variably metering the compressed fluid entering the tubes 47 and 48 for adjusting the speed of response of the vane adjusting mechanism when the latter is controlled by the thermostat T.

Operation of FIGS. 1-7

The compressor C supplies discharge gas through the tube 10 into the condenser 11. Refrigerant liquid flows from the condenser 11 through the tube 12 and the expansion valve EV into the evaporator 14 in which the refrigerant is evaporated. and chills the water circulated through the evaporator. Gas from the evaporator 14 flows through the tube 15 and the low pressure control LPC into the inlet passage 20 of the compressor C, and past the spin vanes 21 into the compressor rotor which is not shown.

Since the solenoid coils SA and SB are, as shown by FIG. 3, normally deenergized, the valve discs 63 and 73 are in the positions shown by FIG. 5, and the piston 26 and the vanes 21 are in hold positions as previously described. When the cooling load is such that the thermostat T calls for additional cooling, its switch LTS closes, and energizes through the closed switch LCS, the solenoid coil SB, causing as shown by FIG. 7, the valve disc 73 to move onto the seat 51, permitting compressed fluid in the cylinder passage 30 to flow through the tube 33 into the chamber 46 of the valve VB, and from the chamber 46 through the tube 52 into the fluid return tube 42, permitting the compressed fluid supplied through.

the valve VA into the cylinder passage 31 to move the piston 26 to the right to adjust the vanes 21 towards open positions, thus increasing the output of the compressor C.

When the temperature of the water flowing through the tube 17 decreases to the operating point of the thermostat switch LTS at the lower end of the dead-band of the thermostat T, the switch LTS opens and deenergizes the solenoid coil SB which causes the valve disc 73 to move from the valve seat 51 onto the valve seat 57 as shown by FIG. 5, preventing the flow of fluid through the return tube 42, and placing the piston 26 and the vanes 21 in hold positions.

When the cooling load decreases, the thermostat switch HTS closes at a temperature at the upper end of the dead-band of the thermostat T, and energizes through the closed switch RS2, the solenoid coil SA, causing as shown by FIG. 6, the valve disc 63 to move onto the seat 50, permitting compressed fluid in the cylinder passage 31 to flow through the tube 34 into the chamber 45 of the valve VA, and from the chamber 45 through the tube 52 into the fluid return tube 42, permitting the compressed fluid supplied through the valve VB into the cylinder passage 30 to move the piston 26 to the left to adjust the vanes 21 further towards closed positions, thus reducing the output of the compressor C. When the thermostat switch HTS reopens as a result of the reduced output of the compressor, it deenergizes the solenoid coil SA, returning the valve disc 63 of the valve VA to the position shown by FIG. 5, and placing the piston 26 and the vanes 21 in hold positions.

When abnormally large current is drawn by the compressor motor CM, the current in the transformer winding 91 increases, and the control 92 energizes the control relays CR1 and CR2. The relay CR1 opens its switch LCS. The relay CR2 closes its switch HCS which energizes the relay R. The latter closes its switches RS1 and RS3 and opens its switch RS2. The closed switch RS1 energizes the solenoid coil SA which acts as described in the foregoing, and as is shown by FIG. 6, to cause the Valve disc 63 to move onto the seat 50, permitting compressed fluid in the cylinder passage 31 to flow through the tube 34 into the chamber 45 of the valve VA, and through the tube 52 into the return tube 42, permitting compressed fluid supplied through the valve VB into the cylinder passage 31) to move the piston 26 to the left to adjust the vanes 21 towards closed positions. At the same time, the closed switch RS3 energizes the solenoid SC which opens the valve VC which supplies compressed fluid from the supply tube 36 through the tube 33 into the cylinder passage 30, in addition to that supplied through the valve VB at this time, thereby providing relatively quick closing of the spin vanes 21 for quickly reducing the abnormal load, which may be temporary, on the compressor motor CM. The open switches LCS and RS2 prevent the solenoid coil SB from being controlled by the thermostat switch LTS at this time. The open switch RS2 prevents the solenoid coil SA from being controlled by the thermostat switch HTS at this time.

If the suction gas pressure decreases to approach the pressure at which the usual low pressure cut-out switch which is not shown, would stop flte compressor motor, the switch LPCS closes and energizes the relay R which closes its switches RS1 and RS3, and opens its switch RS2 to cause, as described in the immediately preceding paragraph, quick closing of the spin vanes 21 for quickly reducing the load on the compressor.

As described in my previously mentioned application, relatively slow adjustment of the spin vanes under control of the thermostat T is desirable for decreasing the tendency of the controls to hunt, and relatively quick closing of the vanes under control of the motor load control 92, and of the low pressure control LPC is desirable for protection when temporary overloads occur.

6 Description of FIG. 8

FIG. 8 corresponds to the upper portion of FIG. 4, and is designed for large systems. In the system of FIGS. 47, there is a tendency for the piston 26 to drift. For example, assume that the vanes 21 have been moving towards open positions due to fluid under pressure flowing into the cylinder passage 31 after having been metered by the screw 82 at a relatively low flow rate. While the cylinder passage 31 has been filling, the cylinder passage 30 has been exhausting. When the thermostat T is satisfied, the piston 26 should be in a hold position. To provide a hold position, fluid must :fill the passage 30 which has been exhausting. In the system of FIGS. 47, the fluid supply to the passage 30 is metered by the screw 88 so that its flow rate is relatively low, causing a time lapse between the time the thermostat T is satisfied and the time the cylinder passage 30 is filled. While the pasage 30 is being filled, the passage 31 is already filled. Until both of the cylinder passages 30' and 31 are completely filled, the piston 26 tends to drift. When the passages 30 and 31 are relatively small as in the case of FIGS. 47, the drifting is unimportant. However, in larger systems where the cylinder passages 30 and 31 are much larger, such drifting is undesired, and the system of FIG. 8 is designed to prevent or substantially reduce such drifting.

In the system of FIG. 8, the metering; screws 81 and 88 and their associated converging walls and 86 respectively, are omitted, the valve VC instead of being connected across the tubes 36 and 33 as in FIG. 4, is connected across the tubes 34 and 42. An adjustable metering valve MV is located in the tube 42 between where the valve VC is connected to the latter, and where the tube 42 connects with the valve VA.

Operation of FIG. 8

FIG. 8 operates as described in the foregoing in connection with control by the thermostat T except that there is no metering of the compressed fluid supplied into the valves VA and VB. The metering valve MV is adjusted to suit operating conditions. When abnormally large current is drawn by the compressor motor CM, or when the suction gas pressure is abnormally low, and the switch HCS or LPCS respectively, closes and energizes the relay R which closes its switches RS1 and RS3 and opens its switch RS2. The solenoid coil SB is deenergized by the open switch RS2 so that the valve VB supplies compressed fluid through the tube 33 into the cylinder passage 30 to move the piston 26 to the left to close the vanes 21. The solenoid coil SA of the valve VA is energized by the closed switch RS1 so that the valve VA is adjusted to connect the cylinder passage 31 to the fluid return tube 42. The solenoid SC of the valve VC is energized by the closed switch RS3, and opens the valve VC which connects the tube 34 directly to the tube 42 downstream of the metering valve MV, causing the cylinder passage 31 to empty quickly to permit quick closing of the vanes 21.

What is claimed, is:

1. A refrigeration system comprising a centrifugal refrigerant compressor, a condenser, an expansion valve and an evaporator connected in a refrigeration circuit, said compressor having an axial suction gas inlet, spin vanes in said inlet, means forming a cylinder passage, means including a piston slidable in said passage for rotating said vanes towards open or closed positions, said passage having a first portion into which fluid under pressure is applied to move said piston in one direction to rotate said vanes towards open positions, said passage having a second portion into which fluid. under pressure is applied to move said piston in the opposite direction to rotate said vanes towards closed positions, a compressed fluid supply tube, a fluid return tube, a first two-way valve connected to said tubes and to said first passage portion,

a second two-way valve connected to said tubes and to said second passage portion, said first valve in a first position routing fiuid from said supply tube into said first passage portion, and in a second position routing fluid from said first passage portion into said return tube, said second valve in a first position routing fiuid from said supply tube into said second passage portion, and in a second position routing fiuid from said second passage portion into said return tube, means including a first solenoid coil for adjusting, when energized, said first valve to its said second position, and for adjusting when deenergized, said first valve to its said first position, means including a second solenoid coil for adjusting, when energized, said second valve to its said second position, and for adjusting, when deenergized, said second valve to its said first position, said coils being normally deenergized, a thermostat having a low temperature switch and having a high temperature switch with a dead-band between said switches, means including said low temperature switch for energizing said second coil, and means including said high temperature switch for energizing said first coil.

2. A refrigeration system as claimed in claim 1 in which said compressor has an electric driving motor, in which relay means responsive to the current drawn by said motor is provided, in which said relay means has a first normally closed switch which opens and has a sec ond normally open switch which closes when abnormally large current is drawn by said motor, in which a normally deenergized relay having third and fourth normally open switches which close and having a fifth normally closed witch which opens when said relay is energized, is provided, in which means including said second switch, when closed, is provided for energizing said relay, in which additional means is provided for energizing said first coil, said additional means including said second and third switches, when closed, in which said means for energizing said second coil includes said first switch, when closed, and said fifth switch, in which said first mentioned means for energizing said first coil includes said fifth switch, in which a normally closed, one-way valve is connected to said supply tube and to said second passage portion, in which a solenoid is provided for opening, when energized, said one-way valve, and in which means including said fourth switch, when closed, is provided for energizing said solenoid.

3. A refrigeration system as claimed in claim 2 in which said circuit includes between said evaporator and said compressor, a low pressure control having a normally open switch which closed when abnormally low suction gas pressures occur, and in which said last mentioned switch is connected across said second switch.

- 4. A refrigeration system as claimed in claim 1 in which said circuit includes between said evaporator and said compressor, a low pressure control having a normally open switch which closes when abnormally low suction gas pressures occur, in which there is provided a normally deenergized relay having first and second normally open switches which close and having a third normally closed switch which opens when said relay is energized, in which additional means is provided for energizing said first coil, said additional means including said switch of said low pressure control and said first switch, when closed, in which said first mentioned means for energizing said first coil includes said third switch, in which said means for energizing said second coil includes said third switch, in which a normally closed one-way valve is connected to said supply tube and to said second passage portion, in which a solenoid is provided for opening said one-way valve, and in which means including said second switch, when closed, is provided for energizing said solenoid.

5. A refrigeration system as claimed in claim 1 in which said compressor has an electric driving motor, in which relay means responsive to the current drawn by said motor is provided, in which said relay means has a first normally closed switch which opens and has a second normally open switch which closes when said relay means is energized by abnormally large current drawn by said motor, in which there is provided a normally deenergized relay having third and fourth normally open switches which close when said relay is energized, in which means including said second switch, when closed, is provided for energizing said relay, in which additional means is provided for energizing said first coil, said additional means including said second and third switches, when closed, in which a normally closed one-way valve is connected to said supply tube and said second passage portion, in which a solenoid is provided for opening, when energized, said one-way valve, and in which means including said fourth switch, when closed, is provided for energizing said solenoid.

6. A refrigeration system as claimed in claim 5 in which said circuit includes between said evaporator and said compressor a low pressure control having a normally open switch which closes when abnormally low suction gas pressures occur, and in which said last mentioned switch is connected across said second switch.

7. A refrigeration system as claimed in claim 1 in which said circuit includes between said evaporator and said compressor a low pressure control having a normally open switch which closes when abnormally low suction gas ressures occur, in which there is provided a normally deenergized relay having first and second normally open switches which close when said relay is energized, in which means including said switch, when closed, of said low pressure control is provided for energizing said relay, in which additional means is provided for energizing said first coil, said additional means including said switch of said low pressure control and said first switch, when closed, in which a normally closed one way valve is connected to said supply tube and to said second passage portion, in which a solenoid is provided for opening, when energized, said one-way valve, and in which means including said second switch, when closed, is provided for energizing said solenoid.

8. A refrigeration system as claimed in claim 1 in which said compressor has an electric driving motor, in which relay means responsive to the current drawn by said motor is provided, in which said relay means has a first normally closed switch which opens and has a second normally open switch which closes when said relay means is energized by abnormally large current drawn by said motor, in which there is provided a normally deenergized relay having third and fourth normally open switches which close when said relay is energized, in which means including said second switch, when closed, is provided for energizing said relay, in which additional means is provided for energizing said first coil, said additional means including said second and third switches, when closed, in which a normally closed one-way valve is connected to said return tube and to said first passage portion, in which a solenoid is provided for opening said one-way valve, and in which means including said fourth switch is provided for energizing said solenoid.

9. A refrigeration system as claimed in claim 8 in which said circuit includes between said evaporator and said compressor a low pressure control having a normally open switch which closes when abnormally low suction gas pressures occur, and in which said last mentioned switch is connected across said second switch.

10. A refrigeration system as claimed in claim 1 in which said circuit includes between said evaporator and said compressor a low pressure control having a normally open switch which closes when abnormally low suction gas pressures occur, in which there is provided a normally deenergized relay having first and second normally open switches which close when said relay is energized, in which means including said switch, when closed, of said low pressure control is provided for energizing said relay, in which additional means is provided for energizing said first coil, said additional means including said switch of said low pressure control and said first switch, when closed, in which a normally closed one-way valve is connected to said return tube and to said first passage portion, in which a solenoid is provided for opening said last mentioned valve, and in which means including said second switch is provided for energizing said solenoid.

References Cited UNITED STATES PATENTS 2,921,446 1/1960 Zulinke 62-117 2,983,111 5/1961 Miner 62-228 X 3,011,322 12/1961 Tanzberger 62,-146 3,081,604 3/1963 Namisniak 62-217 X ROBERT A. OLEARY, Primary Examiner. MEYER PERLIN, Assistant Examiner. 

1. A REFRIGERATION SYSTEM COMPRISING A CENTRIFUGAL REFRIGERANT COMPRESSOR, A CONDENSER, AN EXPANSION VALVE AND AN EVAPORATOR CONNECTED IN A REFRIGERATION CIRCUIT, SAID COMPRESSOR HAVING AN AXIAL SUCTION GAS INLET, SPIN VANES IN SAID INLET, MEANS FORMING A CYLINDER PASSAGE, MEANS INCLUDING A PISTON SLIDABLE IN SAID PASSAGE FOR ROTATING SAID VANES TOWARDS OPEN OR CLOSED POSITIONS, SAID PASSAGE HAVING A FIRST PORTION INTO WHICH FLUID UNDER PRESSURE IS APPLIED TO MOVE SAID PISTON IN ONE DIRECTION TO ROTATE SAID VANES TOWARDS OPEN POSITIONS, SAID PASSAGE HAVING A SECOND PORTION INTO WHICH FLUID UNDER PRESSURE IS APPLIED TO MOVE SAID PISTON IN THE OPPOSITE DIRECTION TO ROTATE SAID VANES TOWARDS CLOSED POSITIONS, A COMPRESSED FLUID SUPPLY TUBE, A FLUID RETURN TUBE, A FIRST TWO-WAY VALVE CONNECTED TO SAID TUBES AND TO SAID FIRST PASSAGE PORTION, A SECOND TWO-WAY VALVE CONNECTED TO SAID TUBES AND TO SAID SECOND PASSAGE PORTION, SAID FIRST VALVE IN A FIRST POSITION ROUTING FLUID FROM SAID SUPPLY TUBE INTO SAID FIRST PASSAGE PORTION, AND IN A SECOND POSITION ROUTING FLUID FROM SAID FIRST PASSAGE PORTION INTO SAID RETURN TUBE, SAID SECOND VALVE IN A FIRST POSITION ROUTING FLUID FROM SAID SUPPLY TUBE INTO SAID SECOND PASSAGE PORTION, AND IN A SECOND POSITION ROUTING FLUID FROM SAID SECOND PASSAGE PORTION INTO SAID RETURN TUBE, MEANS INCLUDING A FIRST SOLENOID COIL FOR ADJUSTING, WHEN ENERGIZED, SAID FIRST VALVE TO ITS SAID SECOND POSITION, AND FOR ADJUSTING WHEN DEENERGIZED, SAID FIRST VALVE TO ITS SAID FIRST POSITION, MEANS INCLUDING A SECOND SOLENOID COIL FOR ADJUSTING, WHEN ENERGIZED, SAID SECOND VALVE TO ITS SAID SECOND POSITION, AND FOR ADJUSTING, WHEN DEENERGIZED, SAID SECOND VALVE TO ITS SAID FIRST POSITION, SAID COILS BEING NORMALLY DEENERGIZED, A THERMOSTAT HAVING A LOW TEMPERATURE SWITCH AND HAVING A HIGH TEMPERTURE SWITCH WITH A DEAD-BAND BETWEEN SAID SWITCHES, MEANS INCLUDING SAID LOW TEMPERATURE SWITCH FOR ENERGIZING SAID SECOND COIL, AND MEANS INCLUDING SAID HIGH TEMPERATURE SWITCH FOR ENERGIZING SAID FIRST COIL. 